Control cells are essential for the accuracy and precision of clinical and immunological assays. They are needed to insure the reliability and accuracy of test equipment and methods and to insure reproducibility through time and from laboratory to laboratory. State and federal regulations which govern such assays often require the use of multi-level controls in order to demonstrate that equipment is performing properly over a range of values. In immunological assays, fresh normal cells have been the standard control cells for such equipment testing. In order to avoid the cost and expense of obtaining and maintaining fresh cells, various methods of preserving fresh cells have been evaluated. For example, U.S. Pat. No. 5,059,518 (the '518 patent) describes the use of lyophilized normal mammalian cells for use as control cells.
Abnormal blood cell samples have also been used as controls to confirm the presence of a disease or determine its stage, but their use has been restricted to fresh or fresh-frozen samples drawn from diseased patients. The supply of such samples is thus inherently restricted. Furthermore, since many of such blood samples are associated with infectious diseases, they are not amenable, for health and social as well as sometimes technical reasons, to large scale production and distribution, and they require special handling procedures. This invention describes an alternative to the use of such abnormal control cells through the use of normal control cell samples which have been modified to reflect the population or count of one or more specific cell types as present in the blood of a person evidencing a specific disease.